| Guido van Rossum | 27e4aa3 | 1997-08-25 15:37:59 +0000 | [diff] [blame] | 1 | """Generic metaclass. |
| 2 | |
| 3 | XXX This is very much a work in progress. |
| 4 | |
| 5 | """ |
| 6 | |
| 7 | import types |
| 8 | |
| 9 | class MetaMethodWrapper: |
| 10 | |
| 11 | def __init__(self, func, inst): |
| 12 | self.func = func |
| 13 | self.inst = inst |
| 14 | self.__name__ = self.func.__name__ |
| 15 | |
| 16 | def __call__(self, *args, **kw): |
| 17 | return apply(self.func, (self.inst,) + args, kw) |
| 18 | |
| 19 | class MetaHelper: |
| 20 | |
| 21 | __methodwrapper__ = MetaMethodWrapper # For derived helpers to override |
| 22 | |
| 23 | def __helperinit__(self, formalclass): |
| 24 | self.__formalclass__ = formalclass |
| 25 | |
| 26 | def __getattr__(self, name): |
| 27 | # Invoked for any attr not in the instance's __dict__ |
| 28 | try: |
| 29 | raw = self.__formalclass__.__getattr__(name) |
| 30 | except AttributeError: |
| 31 | try: |
| 32 | _getattr_ = self.__dict__['_getattr_'] |
| 33 | except KeyError: |
| 34 | raise AttributeError, name |
| 35 | return _getattr_(name) |
| 36 | if type(raw) != types.FunctionType: |
| 37 | return raw |
| 38 | return self.__methodwrapper__(raw, self) |
| 39 | |
| 40 | class MetaClass: |
| 41 | |
| 42 | """A generic metaclass. |
| 43 | |
| 44 | This can be subclassed to implement various kinds of meta-behavior. |
| 45 | |
| 46 | """ |
| 47 | |
| 48 | __helper__ = MetaHelper # For derived metaclasses to override |
| 49 | |
| 50 | __inited = 0 |
| 51 | |
| 52 | def __init__(self, name, bases, dict): |
| 53 | if dict.has_key('__getattr__'): |
| 54 | raise TypeError, "Can't override __getattr__; use _getattr_" |
| 55 | self.__name__ = name |
| 56 | self.__bases__ = bases |
| 57 | self.__realdict__ = dict |
| 58 | self.__inited = 1 |
| 59 | |
| 60 | def __getattr__(self, name): |
| 61 | try: |
| 62 | return self.__realdict__[name] |
| 63 | except KeyError: |
| 64 | for base in self.__bases__: |
| 65 | try: |
| 66 | return base.__getattr__(name) |
| 67 | except AttributeError: |
| 68 | pass |
| 69 | raise AttributeError, name |
| 70 | |
| 71 | def __setattr__(self, name, value): |
| 72 | if not self.__inited: |
| 73 | self.__dict__[name] = value |
| 74 | else: |
| 75 | self.__realdict__[name] = value |
| 76 | |
| 77 | def __call__(self, *args, **kw): |
| 78 | inst = self.__helper__() |
| 79 | inst.__helperinit__(self) |
| 80 | try: |
| 81 | init = inst.__getattr__('__init__') |
| 82 | except AttributeError: |
| 83 | init = lambda: None |
| 84 | apply(init, args, kw) |
| 85 | return inst |
| 86 | |
| 87 | |
| 88 | Meta = MetaClass('Meta', (), {}) |
| 89 | |
| 90 | |
| 91 | def _test(): |
| 92 | class C(Meta): |
| 93 | def __init__(self, *args): |
| 94 | print "__init__, args =", args |
| 95 | def m1(self, x): |
| 96 | print "m1(x=%s)" %`x` |
| 97 | print C |
| 98 | x = C() |
| 99 | print x |
| 100 | x.m1(12) |
| 101 | |
| 102 | |
| 103 | if __name__ == '__main__': |
| 104 | _test() |
| 105 | |
| 106 | |